LTCC inductors have been known and used for several decades. Typically, LTCC inductors are low-power and low-current devices used for RF filters, tuners, and the like. LTCC inductors are not conventionally used for high current applications such as in power supplies or voltage regulators.
LTCC inductors and transformers are made by screen-printing conductive ink patterns (e.g. comprising silver particles) on sheets of green (i.e. unfired) ferromagnetic ceramic material. Multiple green sheets with printed conductor patterns are stacked and then fired at high temperature, causing the sheets and conductive ink to bond by sintering. The printed conductors carry current parallel to the ceramic sheets. Vias filled with conductor paste carry currents perpendicular to the sheets. U.S. Pat. Nos. 5,532,667, 4,785,345, 4,547,961, and 6,914,513 describe examples of various LTCC inductors and transformers. LTCC inductors and transformers are widely used because they are inexpensive, small, and reliable. LTCC inductors also have high magnetic coupling, and accurately tunable magnetic properties.
However, one problem with the known methods for making LTCC inductors is that current and power handling capability is severely limited because the conductors must be applied as a printed film. Typically, the conductive ink is about 0.001″ thick, and the green sheets are about 0.002-0.005″ thick. The conductive ink is applied as a printed film because the green ceramic sheets must be close enough to fuse by sintering. Consequently, the conductive wiring formed from the conductive ink is too thin to carry large currents. These limitations have prevented LTCC inductors from being used in power electronics applications. This is unfortunate because LTCC inductors would otherwise provide many benefits in power electronics applications and other circuits where large currents are present. For example, the small size and high reliability of LTCC inductors make them attractive for use in voltage regulator circuits.
It would be an advance in the art to provide LTCC inductors and transformers that can carry large currents. Such LTCC inductors could be widely used in power electronics circuits and other circuits having large currents.
Voltage regulators are commonly used in power supply circuits for microprocessors, communication electronics and the like. Microprocessors are switched between low-power mode (e.g. “sleep” mode) and higher power modes of operation. Voltage regulators must be able to handle the dramatic changes in operating power consumption, and at the same time maintain high energy efficiency in both high and low power nodes. One significant problem is that microprocessors are typically in low power mode most of the time, and the energy efficiency tends to be very in low power mode.
It would be an advance in the art of power electronics to increase the low power mode energy efficiency of voltage regulator circuits. It would be particularly beneficial to increase the energy efficiency of the low power mode without adversely affecting the energy efficiency of the high power mode.